1. Field of Invention
The present invention relates to the field of well tools. More specifically, the invention relates to a device and method for gravel packing a well that also allows for perforating or fracturing a well in a single trip and that allows full bore access through the device and with weight set down on the device.
2. Related Art
Techniques are well known in the oil and gas industry for controlling sand migration into wells penetrating unconsolidated formations by gravel packing the wells. Sand migration and collapse of unconsolidated formations can result in decreased flow and production, increased erosion of well components, and production of well sand which is a hazardous waste requiring specialized handling and disposal. Such gravel packing typically consists of depositing a quantity, or "pack," of gravel around the exterior of a perforated liner and screen, with the pack preferably extending into the perforations in the unconsolidated formation. The gravel pack then presents a barrier to the migration of the sand while still allowing fluid to flow from the formation. In placing the gravel pack, the gravel is carried into the well and into the formation in the form of a slurry, with much of the carrier fluid or workover fluid being returned to the surface, leaving the gravel in the desired location.
Attempts have been made in the past to minimize the number of trips of the tool string into the well. Each trip of the tool string into a well takes an appreciable amount of time, and therefore incurs significant costs in terms of rig and crew time. As will be readily apparent, these costs are dramatically increased if the tool string is tripped to a great depth in a well. Further, previous devices allow for the use of perforating guns attached to the bottom of the gravel pack tool assembly so that the perforating and gravel pack may be completed in a single trip. The same is true for fracturing equipment which may be attached to prior tool assembles to facilitate fracturing and gravel packing in a single trip.
One problem associated with prior designs relates to control and positioning of the tool assembles. As fluid from the surface is pumped through the tubing and into the well to complete the gravel pack, the tubing tends to shrink due to the temperature differential between the surface and the bottom of the wellbore where the gravel pack is performed. Additionally, other factors may contribute to or cause tubing shrinkage. The tubing shrinkage may create uncertainty as to the positioning of the tool assembly in relation to the packer, sand screen, and other gravel pack components. Some tool assemblies rely on the position of the tool assembly in relation to the fixed downhole components required for the gravel pack to determine the function of and flow paths through the tool assembly. Thus, uncertainty in the positioning of the tool assembly may cause the tool assembly to inadvertently shift from one operation to another. For example, the distance between a circulate position and a squeeze position in one prior tool is only about 18 inches. Shrinkage may move the tool from squeeze to circulate changing the flow paths and operation of the tool. Similarly, in operations performed from a floating platform, the deck heave can change the position of the tool assembly causing uncertainty in the tool assembly positioning. Accordingly, there is a need for a gravel pack tool assembly that eliminates the uncertainty associated with the positioning of the tool assembly and the operating position of the tool assembly.
Another problem associated with prior tool assembles is that they block or restrict the size of the bore through the tool assembly. The restriction limits the ability to perform operations below the tool assembly. For example, in a tool assembly that includes the perforating equipment attached to the bottom of the tool, the manner of actuating the perforating guns is limited. One preferred manner of actuating the perforating guns is to drop a detonation bar through the tubing into engagement with the perforating guns to fire the guns. Typical tool assembles that restrict or block the tubing do not allow a detonation bar to pass therethrough. Thus, the use of a detonation bar in such an operation is not possible. Consequently, despite the use of the prior art features, there remains a need for a tool assembly that provides for full bore diameter through the tool assembly to allow for operations to be performed through the tool assembly, such as logging operations, and/or to allow the passage of well tools, such as wireline and slickline tools, logging tools, chemical cutters, drop balls, detonation/drop bars, and the like, through the tool assembly.